Fuse



D. w. FLoTr-:N 2,287,553

FUSE

June 23, 1942.

Filed April 9, 1958 due to their momentary character.

Patented June 23, 1942 UNITED sTATEs PATENT oFFicE FUSE Donald W.Floten, Chicago, Ill., assigner to Chicago Roller Skate Company,Chicago, lll., a corporation oi' Arizona.

Application April 9, 193s, serial No. 201,079 1o claims. (i. zoo- 135)fore unnecessary to have th'e fuse in such cases blow. In fact, it isdesirable not to have it blow, since the blowing of the fuse under suchcircumstances renders no protection to the circuit and merely wastes thefuse element. Also, the consequent waste of time required to replace thefuse and put the circuit back into operation may in .many instancesconstitute a large loss. While all fuses inherently have some time lagbetween the time the heavy overload starts and the time when the fuseblows, fuses have been made to possess a predetermined time lag of suchextent as to prevent the fuse from being blown by momentary overloadsand yet to blow when overloads are sustained for an. appreciable time.Such a fuse gives the necessary protection for which it is primarilydesigned and also avoids un.-

necessary blowing.

The general object of the invention is to provide a new and improvedfuse element having a time lag sufficient to withstand momentaryoverloads and yet functioning accurately on to aiord the it in which themore or less sustained overloa necessary protection to the ci fuse isplaced.

It is also an important object of the invention to provide a fuseelement having such a time lag,v i which is so constructed that it maybe made of sheet metal of uniform thickness throughout its length anddimensioned so that it may be use in a casing structure of standardsize. f

Another object is to provide a fuse element having fusing sectionsadjacent its respective ends, which sections have sufiicient electricalresistance to generate under a predetermined overload the requiredamount of heat by being made relatively long, thereby ypermitting theelement to' be made of relatively thick metal to give it the desiredtime-lag characteristics and also give it suflicient physical strengthso that it will not be inadvertently bent or distorted in handling. Itis also an object to provide a fuse element,

the fusing sections of which attain the desired heat-generatingresistance by being elongated, with at least a portion Aof each sectionextending laterally of the link to reduce the space longitudinally ofthe fuse required for the fusing section.

A further important object is to provide a fuse element having itsfusing sections so constructed that variations in length, forced uponthe ele' ment .by expansion due' to heat or by variations in length ofthe fuse casing, will not cause the element to bow out of its normalplane.

A still further object is to provide a fuse element constructed so thatits portion of reduced cross-sectionalarea is subjected to a minimumdistortion upon expansion or contraction, thereby avoiding unduecrystallization of the metal and any change in size of such portionsdueto bending or stretching. Y Y Still another object is'to provide afuseelement having a fusing section which is constructed s o that anytendency of an arc to form upon the blowing of the fuse, or the arc tobe maintained, is reduced to va minimum.

Other objects and advantages will become apparent from the followingdescription taken in conjunction with the accompanying drawing, inwhich:

Figure 1 is a sldeview of'a fuse utilizing a fuse eile'ment embodyingthe features of the invent on. L

Fig. 2 is a longitudinal section through the fuse shown in 1.

Fig. 3 is a view with the fuse in the'same position as in Fig. 1 butshowing merely the ltermirial structure with the fuse element connectedthereto.

Fig. 4 is a fview showing the fuse element alone and in a flat position.

while features of the invention may be advantageously used in varioustypes' of fuses, many of its features are particularly useful andadvantageous in a fuse of the cartridge type meet- A ing the standardsboth for physical size and characteristlcs of operation of the NationalBoard of Fire Underwriters. For purposes of illustration,

the fuse element embodying the features of the invention has been shownin a cartridge fuse of the knife blade type.

Asshown herein, this fuse comprises a tubular casing l0 made of nbre orthe like and having at one end thereof a i'errule'l I'threaded into theend of the casing Ill and staked, as at i2, to

hold it against rotation. The ferrule Il is provided with an inwardlyturned flange I3 at its outer end. At the other end' of the casing is aferrule Il threaded into the casing and similarly staked, as at I5. Theouter end of the Iferrule Il is threaded to receive a`cap Ivprovidedwith an inwardly turned flange I1 similar to the flange I3.

The terminal structure of the fuse illustrated herein comprises a pairof knife blades provided with m'eans for closing the ends of the casingcomprising washers 2| secured on the blades. The washers cooperate withthe flanges I3 and I'l in the casing structure to close the latter, andfurther serve to accurately locate the terminal structure within thecasing. The knife blades 20 have inwardly extending portions connectedto each other by a pair of laterally spaced bridge members 22 made 'ofinsulating material, the bridge members being attached to the knifeblades by metallic bridge supports 23. The fuse element, indicatedgenerally at 24, is attached or anchored at its respective ends to theknife blade terminals by a screw 25. The ar-A rangement shown is suchthat each end of the fuse element 24 is lclamped between. adjacent facesof the knife blade terminal and one of the bridge supports 23.Preferably the fuse element is slightly bent out of its plane so that itlies against one face of one of the knife blade terminals and againstthe opposite face of the other terminal. A

- The particular construction of the casing and terminal structureconstitutes no part of the invention but is herein shown merely as anexample of a casing and terminal ystructure of a type meeting therequirements of 'the' National Board of Fire Underwriters/and suitablefor use in connection with a fuse element embodying the features of theinvention.

Q by dimensional requirements for the casing, such i masses of metal canbe obtained solely`by lncreasing the thickness of the element.

In the present instance, a sheet metal fuse element of uniform thicknessthroughout its length is utilized. This thickness is such as to providerelatively large masses of metal functioning to absorb heat generated inthe sections of -the element of reduced cross-sectional area.

Since a fuse blows by virtue of the heat generated in its section orsections of reduced crosssectional area, or by heat imparted theretofrom other sections. the object in designing a fuse element is not toprevent the generation of heat, but rather to generate heat in acontrolled manner. In the present instance two types oi' sections ofreduced cross-sectional area are employed, one of which may serve undercertain operating conditions merely as a heat-generating element, whilethe other type serves as the point which ruptures or fuses. Under otheroperating conditions. the first-mentioned type oi' section serves as thepoint or points of rupture.

'In the fuse element illustrated herein. with particular reference toFig. 4, a pair of fusing sections. indicated by the reference numeral30, is provided, each fusing section having a length indicated. by thebracket. These fusing sections are preferably located adjacent therespective ends of the element, said 'ends being anchored anemona termedan intermediate section 3|. The intermediate section 3l may .in turn beprovided with a plurality of-sec'tions of reduced cross-sectional area.In the present instance such sections are provided by punching in theintermediate sec'- tion a plurality of longitudinally spaced apertures32. The apertures 3l are preferably rectangular in form, leaving aplurality of sections 33 of reduced cross-sectional area along bothedges of the element. 'I'he apertures 32 also leave large masses ofmetal, indicated b'y the numeral 34, at the ends of the intermediatesection, and other relatively large masses, indicated by the numeral 35,between` the apertures.

The masses 34 and 35 serve to absorb heat `generated within the element.Since the sections of reduced area 33 lie along the edges of theelement, verylittle of the current flowing from our section 33 to thenext will dip down into the central portion of the adjacent mass 35because of the increased length of travel. The

masses 35 Athus function chiey as heat-absorbing means, while the bulkof the current will pass along the edges of the element.

When the element is lunder a moderate overload, the heat generated ineach fusing section 30 is conducted and absorbed by the terminalstructure of the fuse and by the mass 34 on the other side. Under thesame operating conditions, the heat generated in the sections 33 isabsorbed chiefly by the masses 3 5. lPreferablythe masses 34 are madegreater than the masses 35 Thus with the larger heat-absorbing abilityof the masses 34 and with the very large heat-absorbing ability of theterminal structure, the fusing sections 30 may be made with greaterheatgenerating capacity than the sectionsA 33. Even with such differencein the heat-generating ca- I pacity, a greater amount of the heatgenerated in the fusing sections 30 will be absorbed than the heat fromthe sections 33.

Under such conditions the sections 30 merely serve as heating sections,the fusing or rupture taking place at one or more of the sections 33.

f' Under larger overloads, the heat-absorbing capacity of .the masses 34and 35 is completely taken up, and the flow of heat from the fusingsections 30 into the terminal structure is insuiliciently fast to takeup the heat generated therein so that the latter, which are of greaterheatgenerating capacity than the sections 33, will become heated andwill rupture.

Since, as mentioned above, the fuse element is made of relatively thickmetal, the masses 34 and 35 have relatively large heat-absorbingcapacity. Thus on momentary overloads,` even though such overloads berelatively large, the masses 34 and 35`are suflicient to absorb enoughof the heat generated in the fusing sections 30 and thesections 33 toprevent blowing thereof. It is only when the overload is sustained anappreciable time that the heat-absorbing capacity of the masses 34 and35 is taken up so that the fuse element will then blow at the desiredoverload to protect the circuit in which it is installed.

In fuse elements heretofore manufactured with such time-lagcharacteristics, the large masses of metal for absorbing heat wereformed by adding metal to the faces of an ordinary sheet metal link.With the construction ofthe fusing sections of such elements, theelement could not be made of particularly thick sheet metal for thereason that by so doing the fusing sections would have to be narrowed'tosuchan extent that they would lack Athe requisite physical strength toditions.

structed, the fusing sections were so shaped that 50 assauts y l 3expands relative to the terminals, the laterally stand handling. Thusthinner sheet metal was used for the element proper and metal was addedto the faces thereof to increase the heat-absorbing capacity.,

The present fuse element is designed so that ksuillcient'physicalstrength-is maintained in the fusing sections and at the same time theelement may be made of relatively thick metal. To this end each fusingsection Il attains its heat-generating resistance by being maderelatively long. 19

With such length it may have a large crosssectional area givingsuillcent physical strength with a thick metal.

In a fuse element ofthe present character, it

is desired to have the intermediate section 3l l5 to provide laterallyextending portions in each fusing section 30 so as to give the requiredlength to attain electrical resistance andat the same time occupy butlittle space longitudinally of the element.

In the preferred form, each fusing section is made by punching a pair ofnotches 40 opposite each other in the respective edges of the element toform a central longitudinally extending portion 36. A rectangularaperture 31 is also punched in the element in parallel relation to thenotches 35 tov form laterally extending portions 38 and thelogitudinally extending edge portions 39 connecting with that part ofthe element which is an- 35 chored to .the terminal structure of thefuse. Thus in each fusing section the portions 38 extend laterally andoppositely to each other to give suilicient'length to provideheat-generating resistance and at the same time to occupy but lit- 40tie space longitudinally of the element. Thev intermediate section ofthe element thus is of maximum length.

In any fuse of this character, variations in relative length between theelement on the one hand and the casing and terminal structure on theother hand occur duetto expansion or contraction under varying heat andmoisture con- In many of the fuses heretofore cona relative increase inlength of the element caused the element to bow laterally. The bowingwould obviously occur in the fusing sections, since these sections arethe weakest physically, so that these sections would be moved toward thecasing or bridge structure. The heat generated. in the fusing sectionswould then tend to burn or char the casing or bridge, both of which areusually made of fibre. Moreover, the bowing would produce rather sharpangular bends in the fusing section which tend to cause the metaltherein to stretch and, under repeated bending, to crystallize. In thecase of a zinc element the metal becomes quite brittle ywhen heated sothat any such distortion would have a bad effect upon the 05 sectionalarea, thereby reducing its electrical rating.

The form of each fusing section 30 is such that any relative expansionof the element occurs in the plane of the element and the distortionoccurring is a minimum. Thus, when the element 76 The metal 20 vof theelement is punched in such a manner as extending portions ll will bendso that the central portion .36 moves toward the aperture 31. Theexpansion is therefore in the plane of the element. Moreover the lengthof the laterally extending portions 38 causes a very slight angular bendrelative tothe central portion 35 and the outer portions 30 so that,while the full amount of expansion of the element is provided for, theactual angular distortion is small. This puts but very little stressupon the metal and thereby avoids the dilculties arising under excessivebending and distortion.

A further advantage is obtained by the structure-of each fusing section30, namely, that, with the laterally extending portions 38, the currentis branched to flow laterally in opposite directions. Such splitting ofthecurrent with its opposite direction of flow sets up opposing magneticfields. On blowing of the fusing section 30 if any arcing occurs, theopposed magnetic fields tend to reduce such arcing. to a minimum.

.From the foregcing it will be evident that l have provided a new fuseelement having a time lag sumcient to 'withstand momentary overloads andyet function accurately on :sustained overloads to afford the necessaryprotection to the circuit in which the fuse is placed. The fuse elementis made of sheet metal cf a single thickness, and is uniform in suchthickness throughout its length and is dimensioned so that it may beused in a casing structure conforming to the requirements oi' theNational Board of Fire Underwriters. The necessary mass of metal in theelement to obtain such time lag is attained by the use of relativelythick metal and the various parts of the element are so constructed thatthey have sufficient physical strength to avoid distortion in handling.The heat-generating resistance in the fusing sections is attained byelongating each of such sections with parts thereof extending laterallyof the fuse element to reduce the space longitudinally of the fuserequired for such sections. The fusing sections are also so constructedthat, upon variation in length of the element, bending out of the normalplane of the element is avoided and a minimum distortion of the metaltakes place. With the laterally extending portions oi' each fusingsection, opposed magneticfields are set up which tend to preventexcessive arcing when the section blows.

I claim as my invention:

l. A fuse element made of sheet metal of unlform thickness comprising apair of fusing sections connected by an intermediate section, eachfusing section being elongated to provide sufficient electricalresistance with a large crosssectional area, and having at least a partextending laterally of the element to provide an intermediate section ofmaximum length.

2. A fuse element comprising a strip of relatively thick sheet metalhaving a pair of fusing sections and an intermediate sectiontherebetween, each fusing section being elongated and having at least apart thereof extending laterally ofthe element whereby both sufficientelectrical resistance and physical strength are attained with the thickmetal and the fusing section is oi minimum dimension longitudinally ofthe element.

3. A fuse element comprising a flat strip of sheet metal having a pairof fusing sections and an intermediate section therebetween,each fusingsection comprising a central portion and a pair of laterally extendingportions providing an elongated fusing section of large cross-sectionalarea for physical strength and occupying a relaand a transverselyextending aperture spaced longitudinally from the notches, the notchesand the' aperture providing therebetween laterally extending portions ofrelatively great length to permit a large cross-sectional area' forphysical strength.

5. A fuse element comprising a iiat strip of sheet metal of uniformthickness and having -a pair oi' opposed notches cut in the respectiveedges of the strip and a transversely extending aperture parallel to thetransverse dimension of the notches to form a fusing section comprisinga central portion branching laterally and then extending longitudinallyof the strip whereby the required electrical resistance is attained bythe length of fusing section with suflicient physs ical strength.

6. In a fuse comprising a lcasing and a pair of terminals, thecombination therewith of a fuse Velement Within the casing connectingthe terminals, said element comprising a strip of sheet metal comprisingend sections for attachment to said terminals, an intermediate section,and fusing sections connecting said intermediate section with therespective end sections, said fusing sections having laterally extendingelongated portions capable of bending in the plane of the strip uponrelative expansion or lcontraction betw'een the casing and the strip toprevent the intermediate section from bending out of the plane of thestrip.

7. In a fuse comprising a casing, a .pair of terminals, and a pair oflaterally spaced bridge members connecting the terminals, thecombination therewith of a fuse element connected at its respective endsto said terminals and located between said bridge members, said fuseelement comprising a pair of fusing sections Aand an intermediatesection therebetween, said fusing sections having laterally extendingelongated portions capable of bending in the plane of the element uponrelative expansion or contraction between the bridge members and theelement to prevent the intermediate section from bendingv toward saidbridge members.

8. A fuse element comprising a-strip of sheet metal having a pair ofopposed rectangular notches in the respective edges of the strip toprovide a central longitudinally extending tongue, and having 'arectangular aperture in parallel relation to the notches to lprovideportionsV xtending laterally `from the tongue and portions extendinglongitudinally from the outer' ends of the laterally extending portions.

9. A fuse element comprising a pair of terminal sections, anintermediate section of relalocated at the respective ends of theintermediate section, each fusing section having at least a part whichis elongated and extends laterally of the strip.

f DONALD W. FLOTEN'.

